Why does cropping reduce dynamic range? (Page 3): OK that makes sense, and also seems to answer Larry's question about crop camera vs. cropping full frame.

bleirer

Ysarex wrote:

Yes.

The noise is always there. The noise that we're concerned about in this case and that limits DR is shot noise. It's in the signal and it's always in the signal. For us to see it we have to enlarge the image.

OK that makes sense, and also seems to answer Larry's question about crop camera vs. cropping full frame.

Ysarex Loc: St. Louis

lamiaceae wrote:

That is probably a good explanation though I more or less think of sensor characteristics per pixel or photo site. So a function of pitch as well. But as I have heard before, much of the science of digital photography is related to audio engineering, signal and noise, and less to traditional film based photography. But your explanation seems to cover it.

Pixel pitch is a factor and has to be considered when comparing different sensors. In this case given Bleirer's OP question we're in fact dealing with the very same sensor and so the same pixels.

Pixel pitch/size relates to read noise in the sensor. Sensor size relates to shot noise in the signal. Both are involved when we look at how much more noise is apparent in different size sensors. What we need to keep in mind is that one of those is a much bigger factor than the other. The read noise difference due to pixel size is minor -- possibly to the point of insignificance when compared to the shot noise difference. Here's a good article that addresses that: https://www.dpreview.com/articles/5365920428/the-effect-of-pixel-and-sensor-sizes-on-noise/2

bclaff Loc: Sherborn, MA (18mi SW of Boston)

bleirer wrote:

...
So why does cropping alone reduce dynamic range?

Photographic Dynamic Range (PDR) is normalized to a standard image size and viewing conditions.
The DX (APS-C) capture must be enlarge more than the FX (FF) one.
For some details see DX Crop Mode Photographic Dynamic Range

bleirer

bclaff wrote:

Photographic Dynamic Range (PDR) is normalized to a standard image size and viewing conditions.
The DX (APS-C) capture must be enlarge more than the FX (FF) one.
For some details see DX Crop Mode Photographic Dynamic Range

That makes sense, so as Ysarex said, if one just took a crop out of a full frame sensor image without resizing there would be no impact?

Ysarex Loc: St. Louis

bleirer wrote:

That makes sense, so as Ysarex said, if one just took a crop out of a full frame sensor image without resizing there would be no impact?

It's just that simple. In which photo of superman below do you see noise? You see the noise when you enlarge the noise.

(Download)

a6k Loc: Detroit & Sanibel

Count me as a denier. The dynamic range of a sensor is no different than the DR of each pixel array. If the "test" is saying otherwise then there is a problem with definitions.

The DR of each pixel is measured in "stops" from fully saturated to minimally saturated but able to produce a readable result. Many factors are at work, but the number of pixels should not be. The amplification before or after read/A-D conversion is a factor but it still affects all the pixels equally (if anyone thinks otherwise please provide data).

When ISO is increased it shortens the DR. Some cameras such as my 𝜶6500 are exhibiting strange non-linearity in this regard due to some kind of change in amplification. But generally, that relationship is reasonably linear for each camera and in the case of my camera, it is true but with a jog.

The idea that sampling only the central portion of the sensor would change the DR is simply wrong. If some test is saying that then the test is either being done wrong or is being read wrong.

selmslie Loc: Fernandina Beach, FL, USA

Ysarex wrote:

Noise increases because of the different total areas of the sensor used. ...

That's not true because every part of the sensor got the same exposure, the part that's inside the crop and the part that's left out.

Compare a thumbnail to a downloaded image. You might see the noise in the full image, especially enlarged to 100%. But you will be hard-pressed to see it in the thumbnail.

The reason it looks noisier is simply because, when you view the resulting image, you have to enlarge the cropped version more than the full version. That makes the noise easier to see.

The same thing would happen if you cropped the full frame image after you captured it.

For example, if you enlarge a full frame image to 8x12 it's approximately an 8½x enlargement. If it's cropped by 1.5x during post processing it needs 12.75x enlargement. The extra enlargement makes the noise easier to see.

PS: I see you just corrected your error. https://www.uglyhedgehog.com/t-687091-3.html#12031291

TriX Loc: Raleigh, NC

bclaff wrote:

Photographic Dynamic Range (PDR) is normalized to a standard image size and viewing conditions.
The DX (APS-C) capture must be enlarge more than the FX (FF) one.
For some details see DX Crop Mode Photographic Dynamic Range

👍👍 Thanks for providing the definitive answer Bill.

Ysarex Loc: St. Louis

selmslie wrote:

That's not true because every part of the sensor g... (show quote)

I see that you just validated my claim that you originally misunderstood.

In case you'd like to understand why I was right in the first place: https://www.dpreview.com/articles/8189925268/what-s-that-noise-shedding-some-light-on-the-sources-of-noise

selmslie Loc: Fernandina Beach, FL, USA

Ysarex wrote:

I see that you just validated my claim that you originally misunderstood.

In case you'd like to understand why I was right in the first place: https://www.dpreview.com/articles/8189925268/what-s-that-noise-shedding-some-light-on-the-sources-of-noise

Your original claim about the area of the sensor was wrong. So was the claim that the larger sensor got more light thereby reducing the noise.

Ysarex Loc: St. Louis

a6k wrote:

Count me as a denier. The dynamic range of a senso... (show quote)

DR is noise limited. We identify the low end limit of available DR as the point where signal can no longer be recognized as separate from noise.

Larger sensors are less noisy than smaller sensors because larger sensors record more total light than smaller sensors. If you crop and only use the center portion of a sensor you're using less total light and so increasing noise and so decreasing DR.

Ysarex Loc: St. Louis

selmslie wrote:

Your original claim about the area of the sensor was wrong. So was the claim that the larger sensor got more light thereby reducing the noise.

I just gave you a link to read that validates my original assertion. This is common knowledge. Here's a quote from the article: "As a result, when you shoot two different sized sensors with the same shutter speed, f-number and ISO, the camera with the smaller sensor has to produce the same final image brightness (which the ISO standard demands) from less total light. And, since we've established that capturing more light improves your signal-to-noise ratio, this means every output tone from the larger sensor will have a better signal-to-noise ratio, so will look cleaner."

Here's the article: https://www.dpreview.com/articles/8189925268/what-s-that-noise-shedding-some-light-on-the-sources-of-noise

Larger sensors record more total light than smaller sensors and more total light = better SNR and so less noise. DR is noise limited.

selmslie Loc: Fernandina Beach, FL, USA

Ysarex wrote:

... Larger sensors are less noisy than smaller sensors because larger sensors record more total light than smaller sensors. If you crop and only use the center portion of a sensor you're using less total light and so increasing noise and so decreasing DR.

So you still don't understand the issue. We are talking about the same sensor with two different crops.

As several of us have pointed out, including Bill Claff, it's the enlarging of the result that makes the noise more visible.

What's odd is that you even demonstrated exactly that. Then you went back to your original error.

You can't have it both ways.

bleirer

Thanks for all the replies. I'm satisfied with the answers given.

Ysarex Loc: St. Louis

selmslie wrote:

So you still don't understand the issue. We are talking about the same sensor with two different crops.

As several of us have pointed out, including Bill Claff, it's the enlarging of the result that makes the noise more visible.

What's odd is that you even demonstrated exactly that. Then you went back to your original error.

I did not make an original error. This statement is correct and as I said it's common knowledge: "Larger sensors are less noisy than smaller sensors because larger sensors record more total light than smaller sensors. If you crop and only use the center portion of a sensor you're using less total light and so increasing noise and so decreasing DR."

Again from the article I linked:
The effect of sensor size

There are three factors that affect how much light is available for your sensor to capture: your shutter speed, f-number and the size of your sensor.

As we showed in our equivalence article, a full frame camera shot at 85mm F5.6 and a Four Thirds camera at 42.5mm F2.8 will have the same angle of view and the same aperture size (15.2mm diameter) and hence will be exposed to the same amount of light if exposed for the same amount of time. Or, put another way, at the same f-number (both cameras set to F2.8), the full frame camera will see four times as much light as a camera with a Four Thirds sensor, since it is exposed to the same light-per-unit-area but has a sensor with four times the area.

As a result, when you shoot two different sized sensors with the same shutter speed, f-number and ISO, the camera with the smaller sensor has to produce the same final image brightness (which the ISO standard demands) from less total light. And, since we've established that capturing more light improves your signal-to-noise ratio, this means every output tone from the larger sensor will have a better signal-to-noise ratio, so will look cleaner. [may bold]

And again here's the article: https://www.dpreview.com/articles/8189925268/what-s-that-noise-shedding-some-light-on-the-sources-of-noise

What I said is correct and I've presented a recognized reference to back it up.